Pleural effusion due to pulmonary emboli.

Pulmonary embolism is the fourth leading cause of pleural effusion. The possibility of pulmonary embolus should be evaluated for all patients who have undiagnosed pleural effusion. The mechanism of pleural effusion caused by pulmonary embolus is usually increased interstitial fluid in the lungs as a result of ischemia or the release of vasoactive cytokines. Approximately 75% of patients with pulmonary emboli and pleural effusion have pleuritic chest pain. The most common cause of pleuritic chest pain and pleural effusion in patients under 40 years old is pulmonary emboli. Pleural effusion resulting from a pulmonary embolus usually occupies less than one-third of the hemithorax. Dyspnea is frequently out of proportion to the size of the pleural effusion. Pleural fluid caused by pulmonary emboli is usually exudative but is occasionally transudative. d-Dimer testing is a good screen for pulmonary emboli. If d-dimer results are positive, then a spiral computed tomograph should be obtained to confirm the diagnosis. Low-molecular-weight-heparin has become the initial treatment of choice for patients with pulmonary emboli and pleural effusion.